Grover Rotomatic 406C locking guitar tuning machine heads give you easy tuning and positive string locking. With a gear ratio of 18:1, these locking tuners serve up all the goodness of standard Rotomatics - plus Grover's internal cam post. Stick the string through the string hole, hand pull to tension, and begin tuning. As you start to tune, only the locking cam inside the string post turns.